Mineral fibers made by melting and spinning of mineral raw materials, such as rock, slag and the like, are to a great extent used for the manufacture of mineral fiber mats and blankets, primarily for heat and sound insulation purposes within the construction industry. In addition to the formed mat exhibiting good insulation characteristics with respect to heat and sound, increasingly more importance has been recently attached to the characteristics of the mat from the viewpoint of health, primarily of industrial hygiene. This has lead to attention being directed increasingly more to developing fiber which are soluble in biological fluids in order to ensure that fiber particles, which are not transported out of the body, dissolve in the body fluid.
Thus e.g. the patent application WO 89/12032 describes a fiber composition which exhibits an increased solubility in physiological saline solutions. According to the specification, the components in the said compositions may vary within wide limits, but according to the specification, an increase in the amount of amphoteric oxides, i.e. of aluminium, zirconium and titanium, tends to increase the stability of the compositions against extraction. Even though the application does not at all discuss the effects of the presence of phosphorus, there is included an example of a composition containing a little over 6% by weight of P2O5, in combination with a low content of Al2O3. This composition exhibits a fairly good solubility, primarily due to the small amount of Al2O3 present.
According to the present invention it has now been discovered that compositions which contain aluminium and/or iron oxides, as well as phosphorus oxide, and wherein the weight ratio of phosphorus to the sum of aluminium and iron, all calculated as their oxides, lies within a fairly narrow range, surprisingly exhibit very favourable solubility characteristics in physiological saline solutions.
The object of the present invention is thus a mineral fiber composition which is soluble in biological fluids and which is characterized in that it contains substantially
45-65% by weight of SiO2 
15-40% by weight of CaO
0-20% by weight of MgO
0-6% by weight of Na2O+K2O
and in addition aluminium and/or iron oxides as well as phosphorus oxide in such amounts that the weight ratio of P2O5 to the sum of Al2O3 and iron oxide is circa 0.4 to 6.
The total amount of Al2O3 and iron oxide is preferably at least circa 0.5, advantageously circa 0.5 to 7% by weight and the weight ratio is preferably circa 0.5 to 2.
The object of the invention is also a method for increasing the solubility of mineral fiber compositions which method is characterized in that to a mineral composition having a total Al2O3 and iron oxide content of at least circa 0.5% by weight, phosphorus is added in such an amount that the weight ratio of P2O5 to the sum of Al2O3, and iron oxide is circa 0.4 to 6, optimally circa 0.5 to 2.